Device for creating a beam of adjustable-energy ions particularly for sequential vacuum treatment of surfaces with large dimensions

ABSTRACT

A device for generating an ion beam, particularly for the continuous processing of large surfaces, includes an ionising chamber with a gas being fed thereinto to be acted upon by a high frequency alternating electrical field, extraction optics capable of extracting ions from the ionising chamber and generating an ion beam from the device, and excitation means capable of creating the high frequency alternating electrical field within the ionising chamber through a connection, by a waveguide, to a microwave generator. The excitation means include a conductive enclosure engaging one wall of the ionising chamber, wherein the inner space of the conductive enclosure is divided into a first portion, opposite the ionising chamber, to which the waveguide is connected, and a second portion, adjacent the ionising chamber, in which cylindrical conductive cavities are uniformly distributed, with each cavity comprising an adjusting means for adjusting the amount of microwave energy passing through that cavity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for creating a beam ofadjustable energy ions particularly for sequential vacuum treatment ofsurfaces with large dimensions.

2. Description of Related Art

For treatment of automobile sheet metal in particular, to improve itscorrosion resistance, it is known to bombard it with ions obtained byionization of an appropriate gas such as nitrogen. Sequential treatmentof a piece of sheet metal consists of moving the latter in the field ofa fixed ion beam so that the beam of ions sweeps the entire surface ofthe metal. Depending on the density of the ion beam, the metal is movedat an appropriate rate to achieve the desired bombardment.

In order to implement this technique, it is preferable to have a verywide beam of ions. In this case, however, the problem arises ofgenerating a beam of ions that is sufficiently dense and uniform overits entire width.

SUMMARY OF THE INVENTION

The goal of the present invention is to furnish a device able to providea dense, wide beam of ions with good homogeneity that is particularlysuited for sequential treatment of surfaces with large dimensions. Thepresent invention relates to a device for creating a beam of ionsparticularly for sequential treatment of surfaces with large dimensions,having an ionization chamber into which a gas can be introduced to besubjected to the action of an alternating high-frequency electricalfield, extraction optics able to extract ions from the ionizationchamber and emit a beam of ions from the device, and excitation meansable to establish the alternating high-frequency electrical field insidethe ionization chamber, being connected by a waveguide to a microwavegenerator, characterized in that said excitation means include aconducting enclosure abutting a wall of the ionization chamber, theinterior of this enclosure being divided into a first part opposite theionization chamber in which the waveguide terminates and a second partadjacent to the ionization chamber that contains essentially identicalcylindrical conducting cavities open at both their ends, the lengthwiseaxes of said cavities being parallel to each other and perpendicular tosaid wall of the ionization chamber, each cavity having an adjustingelement to adjust the quantity of microwave energy passing through saidcavity.

According to the invention, "cylindrical cavity" is understood to be acavity with a constant cross section. This cross section can be of anyshape, preferably rectangular. It will be understood that the excitationmeans according to the invention constitute a power divider which hasthe function of distributing the energy furnished by the microwavegenerator among the various cavities, each of which constitutes anindependent waveguide that radiates into said ionization chamber at itsaperture adjacent to the ionization chamber. Since the cavities aresubstantially identical, each emits the same quantity of energy into theionization chamber. In addition, since the cavities are regularlydistributed in the enclosure, the electrical field generated in theionization chamber exhibits good homogeneity.

In a preferred embodiment of the invention, the cavities are aligned intwo rows parallel to the large dimension of the surface of theionization chamber located opposite the extraction optics, and aredisposed in a staggered arrangement in these two rows. In thisembodiment, displacement of the parts to be treated, in a directionperpendicular to the two rows of cavities, improves the homogeneity ofthe ionic treatment of each part still further, since the less-denseareas of the first row are compensated by the denser areas of the secondrow, and vice versa.

According to the invention, the ionization chamber is separated from theconducting enclosure by a dielectric window impermeable to the gases tobe ionized and permeable to electromagnetic waves. If it is subjected tothe action of any metal particles emitted by the surface of the partduring treatment, the dielectric window tends to metallize and hencelose its dielectric properties. As a result, the efficiency of thedevice may be impaired. It is thus necessary to replace said dielectricwindow, said replacement posing no problem for devices with smalldimensions.

On the other hand, the device according to the invention has a largedielectric window which is an expensive, difficult-to-replace part. Toovercome this disadvantage in a preferred embodiment of the invention,the axis of the extraction optics is inclined relative to the lengthwiseaxis of the device in order to prevent any metal particles emitted bythe surface of the part during treatment from reaching said dielectricwindow.

In a preferred embodiment of the invention, the outer wall of theionization chamber has permanent magnets that create a static magneticfield in the ionization chamber. Because of the combination of thealternating electrical field and the static magnetic field, ionizationefficiency is increased by the known phenomenon of cyclotron electronresonance.

BRIEF DESCRIPTION OF THE DRAWINGS

For better understanding of the invention, two embodiments will now bedescribed, provided as non-limiting examples with reference titheattached drawing wherein:

FIG. 1 is a perspective view of a device according to a first embodimentof the invention,

FIG. 2 is a cross-sectional view along II--II of FIG. 1,

FIG. 3 is a view similar to FIG. 1 of a device according to a secondembodiment of the invention, and

FIG. 4 is an enlarged cross-sectional view along IV--IV in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The device shown in the drawing has an ionization chamber 1 into which agas can be introduced through an orifice 2. Chamber 1, which isparallelepipedic, is elongate in a direction X. Extraction optics 3preferably having three grids are placed in front of one of the faces 1aof the ionization chamber. The axis of the grids is parallel to thelengthwise axis of the device.

On its face 1b opposite face 1a, the ionization chamber has a wall madeof a dielectric material permeable to microwaves, quartz for example,which constitutes a vacuum-tight and hence a gas-tight dielectric windowin the sense of the invention. Permanent magnets 5 are disposed on thelong sides 1c of the ionization chamber. In known fashion, two adjacentmagnets have opposite polarities.

A power divider 6 is applied against face 1b of ionization chamber 1.This power divider 6 has an electrically conducting enclosure 7, shownin dashed lines, with the same cross section as ionization chamber 1.According to the invention, the interior of enclosure 7 is divided intoa first part 8 opposite ionization chamber 1 and a second part 9contiguous to the first part and adjacent to ionization chamber 1.

A waveguide 10 terminates inside enclosure 7 in its first part 8. Thiswaveguide 10 is connected to an impedance matching device 11 whichadvantageously has three tuning plungers 11a, and is itself supplied bya microwave generator, not shown. The second part 9 of enclosure 7 hascylindrical conducting cavities with a rectangular cross section andwith the same dimensions, which are formed by a single wall 12 parallelto direction X and extend over the entire length of enclosure 7, and bypartitions 13 perpendicular to wall 12 disposed on either side of saidwall. Wall 12 and partitions 13 are electrically conducting.

In the cross-sectional view of FIG. 2, it can be clearly seen thatcavities 14 thus defined in the second part 9 of enclosure 7 have thesame dimensions. Cavities 14 are thus aligned in two parallel rows 15aand 15b and are also disposed in a staggered arrangement in these tworows. In this way, when parts to be treated move in a direction Yperpendicular to direction X, they are sequentially subjected to theaction of the first beam of ions coming from row 15a and to that of asecond beam of ions coming from row 15b such that the two successive iontreatments are superimposed, allowing any lack of homogeneity in thebeam of each row to be offset, particularly between the central regionsof cavities 14 and the adjacent regions of walls 12 and partition 13.

In order to ensure good distribution of microwave energy between thevarious cavities 14, enclosure 7 also has, on its long sides, adjustingscrews 16 each of which terminates in a cavity 14. The part of eachadjusting screw 16 that terminates in corresponding cavity 14constitutes an obstacle to the passage of the microwaves such that byturning this screw 16 to a greater or lesser degree, the quantity ofenergy passing through said cavity 14 is adjusted. Thus, the cavitiesfurthest from the opening of waveguide 10 can radiate into ionizationchamber 1 substantially the same quantity of energy as do the cavitieslocated in the vicinity of the end of waveguide 10.

Due to the staggered arrangement of cavities 14 in the two rows 15a and15b, small unused spaces 17 remain at one end of each row. The size ofone of these spaces 17, in direction X, is equal to half the length of acavity 14. In the embodiment shown, unused spaces 17 are occupied byconducting wedges 18 made of brass or aluminum, with asemiparallelepipedic shape, truncated in a diagonal plane. Wedges 18 aredisposed in each space 17 with their bases abutting wall 4 of theionization chamber. Thus the cross section of each wedge 18 increasesfrom the interface between parts 8 and 9 of enclosure 7 in the directionof ionization chamber 1. In this way, any reflections of waves in thefirst part 8 of the enclosure that could interfere with energydistribution between cavities 14 is avoided.

In the example illustrated, the dimension of the device in direction Xis approximately 50 cm and in direction Y, approximately 4 cm.

FIGS. 3 and 4 show a second embodiment of the invention in whichextraction optics 3', also made of three grids, are positioned with axisΔ₁ inclined relative to lengthwise axis Δ₂ of the device. For thispurpose, ionization chamber 1' has the shape of a semiparallelepipedwhose cross section is a rectangle and whose front face 1'a is inclinedrelative to its rear face 1'b, as can be seen in FIGS. 3 and 4.

As shown in the cross-sectional view in FIG. 4, this arrangement ofextraction optics 3' prevents any metal particles emitted by the surfaceof a part 20 subjected to a beam of ions delimited by dot-dashed lines21 from reaching gas-tight window 4. It can be seen that trajectories 19of the metal particles that pass through extraction optics 3 in thedirection opposite that of the ion beam arrive at one of side walls 1'cof ionization chamber 1'. Hence, only this wall 1'c is able tometallize, which has no effect on formation of the ion beam. On theother hand, since gas-tight wall 4 is not impinged upon by metalparticles, it retains its dielectric properties. It is hence no longernecessary to replace it.

It goes without saying that the embodiment that has just been describedis not limiting in nature and may receive any desirable modificationswithout thereby departing from the scope of the invention.

We claim:
 1. A device for creating a beam of ions, comprising:anionization chamber into which a gas can be introduced; excitation meansfor subjecting the gas introduced into the ionization chamber to analternating high-frequency electrical field to generate ions from thegas; and extraction optics capable of extracting ions from theionization chamber and emitting a beam of the ions from the device;wherein the excitation means comprises a conducting enclosure abutting awall of the ionization chamber, the conducting enclosure comprising:afirst portion adjacent to the ionization chamber, and a second portionspaced from the ionization chamber by the first portion, wherein thefirst portion comprises a plurality of identically-shaped conductingcavities, each conducting cavity having a constant cross-section andopened at each end, a lengthwise axis of each of the plurality ofconducting cavities being parallel to each other and being perpendicularto the wall of the ionization chamber, each conducting cavity having anadjusting element that adjusts a quantity of energy of the alternatinghigh-frequency electrical field passing through the cavity.
 2. Thedevice of claim 1, wherein the second portion of the conductingenclosure is connectable to a first end of a waveguide, a second end ofthe waveguide connected to a microwave generator generating microwaveenergy which passes through the waveguide into the second portion of theconducting enclosure, the adjusting element of each cavity capable ofadjusting a quantity of the microwave energy passing through thatcavity.
 3. The device of claim 1, wherein an axis of the extractionoptics is inclined relative to a lengthwise axis of the device.
 4. Thedevice of claim 3, wherein the extraction optics directs the beam ofions against a metal object having a large dimension.
 5. The device ofclaim 3, further comprising a dielectric window separating theionization chamber from the conducting enclosure, an inclination of theinclined axis of the extraction optics preventing metal particlesemitted from a surface of the metal object from reaching the dielectricwindow.
 6. The device according to claim 1, wherein the plurality ofcavities are arranged into two rows, each row parallel to a lengthwisedirection of the ionization chamber, the cavities of a first one of thetwo rows offset relative to the cavities of a second one of the tworows.
 7. The device of claim 1, further comprising a plurality ofpermanent magnets disposed on a second wall of the ionization chamberextending between the excitation means and the extraction optics, theplurality of permanent magnets creating a static magnetic field in theionization chamber.
 8. The device of claim 1, wherein the plurality ofcavities are formed by:a wall of the excitation means extending along alength of the first portion of the excitation means and which extendsbetween the ionization chamber and the second portion; and a pluralityof partitions extending perpendicularly from the wall of the excitationmeans, the plurality of partitions disposed on both faces of the wall ofthe excitation means.